Dr Tony Perry, co-creator of Xena"Pigs have a great potential for their use as organ donors" real 28k

Wednesday, 16 August, 2000, 18:05 GMT 19:05 UK

Fresh doubt on pig organ safety

PPL's pig clones were announced in March

The possible dangers of using pig organs for transplant into humans have been highlighted again by scientific research.

Mice given pig pancreatic cells in the laboratory became infected with a porcine retrovirus.

Although the rodents appeared to suffer no ill effects, scientists say they cannot predict the result if the infection were to get into humans.

The research, published in the journal Nature, comes as two leading centres report successful attempts to use cloning technology to create pigs whose organs would be better suited to xenotransplantation.

Mood of concern

Scientists in Japan, reports Science magazine, have produced a pig clone named Xena from genetic material drawn from foetal pig skin.

Lead scientist Akira Onishi shows off Xena to the world

And the Scottish-based company PPL Therapeutics, has produced five pig clones created with a slightly different technique. These pigs were actually presented to the world in March.

However, the virus study, by Dr Daniel Salomon from the Scripps Institute in La Jolla, US, is certain to add to the mood of concern surrounding the safety of xenotransplantation.

His team tried to reproduce the circumstances of xenotransplantation, except the recipients of the pancreatic cells were mice whose immune systems had been weakened in preparation for the transplant.

Active retroviruses

When the mice were tested, porcine endogenous retroviruses - infections normally specific only to pigs - were found to be both active and spreading in the mouse tissues.

Exact copies: Pig embryo clones before implantation

In a separate experiment, the team showed that the viruses were capable of doing the same thing in human tissue in the lab.

The findings reinforce those of a study published in 1997 by Professor Robin Weiss, an expert in retroviruses now working at University College London.

He said: "It makes it doubly clear that we should be being very careful indeed about transplanting these organs into humans."

He added, however, that there was still "massive potential" in the future for xenotransplantation, as supplies of suitable human organs would never be sufficient.

Other studies have been more positive about the risks of retrovirus transmission via xenotransplants.

One looked at more than 100 patients who had all been exposed to living pig cells for various reasons, and found none had any signs of infection.

Increased supply

Many scientists are still trying to find a way of boosting the supply of suitable organs from human sources.

The increased safety of modern cars, alongside the advent of seatbelt legislation, mean that the main source of organs has been diminished in recent years.

A report in the journal Clinical Transplantation this week found that using livers taken from older donors was just as effective as taking them from the young - which is the standard practice.

But Professor Weiss said that many desperately ill patients awaiting transplants would probably be willing to take the chance that xenotransplants would cause illness - because they were dying anyhow from their organ failure.

And Dr Tony Perry, of Rockefeller University, US, a co-worker on the Xena experiments, said it was worth pursuing such research despite the risk that diseases could leap from pigs to humans.

"One should never be complacent about these risks," said Dr Perry.

"We who are interested in the possibility of xenotransplantation to meet this shortfall in organs are very pleased that researchers are flagging up the potential problems so we can move forward and address them."